Elastic shirring of the garments in selected regions is desirable or essential in order that the garment will conform to the body of the wearer such as at the waist or wrist. This feature is especially true with respect to disposable garments, including plastic garments such as disposable diapers. Hence, the invention, its background and several embodiments, will be described with particular reference to disposable diapers or incontinence garments, but it is understood that the invention is applicable to other garments such as gowns, masks, shoe covers, etc.
Disposable diapers typically have an "hour glass" or general "I-shaped" configuration. The diapers are produced from a continuous web of inner and outer facing sheets and an absorbent batt wherein each waistband area of a diaper module is integrally connected to the waistband area of immediately adjacent diaper modules. (In this regard, see FIG. 2.) The web is cut at the waistband area transverse to the web travel direction to thereby form individual diapers. Thus, the waistband is cut in a cross-machine direction.
Application of elastomeric material to the legbands of disposable diapers has been commercially achieved. However, when elastomeric material is attempted to be applied to waistbands on the same diaper having the legband attached, significant production problems arise. For example, if tension is maintained in the legband direction, the elastomer attached to the waistband tends to bunch the diaper and thus interfere with folding, packaging or other production sequences. We know of no commercial solution to the production problems described above.
Recently, certain proposals have been made regarding heat-set, heat-shrinkable elastomeric materials for use in effecting shirring of disposable garments such as disposable diapers or hospital gowns as evidenced by U.S. Pat. Nos. 3,912,565; 3,819,401; and 3,639,917.
U.S. Pat. No. 3,912,565 to Koch, et al. and U.S. Pat. No. 3,819,401 to Massengale, et al. disclose that flexible polyurethane and plasticized vinyl chloride sheet materials, respectively, are heated, stretched, and cooled to prevent premature shrinkage. In order to prevent premature shrinkage, the elastomeric sheet materials are again heated to permit limited relaxation and cooled to heat set the sheet materials. The heat set sheet materials are then applied to articles and upon application of heat, they shrink to their original lengths thus shirring the articles. As more fully explained with reference to FIG. 1 in Koch, et al. and Massengale, et al., the sheet material is stretched between heated roll 25 and nip rolls 31, 33, then cooled, partially relaxed in heated liquid bath 45 and collected in roll 49. What should be noted in Koch, et al. and Massengale, et al. is that stretching is accomplished by application of external heat, cooled at the stretched condition, then again heated by application of external heat to effect controlled heat shrinkage. U.S. Pat. No. 3,639,917 to Althouse discloses an elastomer comprising block copolymers that are heat-shrinkable. According to Althouse, the block copolymers are expanded or deformed from an original length at elevated temperatures to achieve a new length and then cooled to maintain the copolymers at the new length of the expanded state. The copolymers of Althouse retain the new length until again heated, at which time shrinkage to the original length occurs. The copolymers of Althouse therefore are expanded from their original length to a new length, maintained at the new length by cooling, and subsequently returned to the original length upon application of heat.